Windows NT processor scheduling

Without processor scheduling the Microprocessor would give attention to jobs based on when they arrived in the queue. This is not always optimal. Some applications should be given more time with the processor because that program is more critical. In order to do this, the processor give a priority level to different processes running on the machine. When two processes are requesting service at the same time, the processor performs the jobs for the one with the higher priority.

There are six named priority levels: • Realtime • High • Above Normal • Normal • Below Normal • Low

These levels have associated numbers with them. Applications start at a base priority level of eight. The system dynamically adjusts the priority level to give all applications access to processor. Priority levels 0 - 15 are used by dynamic applications. Anything running at a dynamic level can be written to the Windows NT Pagefile. This includes user application by default and operating system functions that are not imperative to the performance of the operating system. Priority levels 16- 31 are reserved for real-time applications that cannot be written to the Windows NT Pagefile. Because of this, they will not be paged to disk and will reside in main memory.